Preparation of polyester amides with cadmium acetate catalyst



UnitedStates Pa ent This invention is addressed to the general subject matter of polyestei amide preparations. More particularly, it is concerned with an improved method for obtaining polyesteramides by poly-condensing terephthalic acid diamide- N,N die-caproic acid or its ester derivatives with a glycol -"in the presence of a novel catalyst.

It is known that a superior polyesteramide can be prepared from terephthalic acid diamide-N,N-di-e-caproic Howacid or its ester derivatives and ethylene glycol. ever, previously known procedures for preparing these polymers have not been economic and the polymers obtained therefrom have been greatly discolored. These shortcomings have been for the most part due to the unavailability of efficient catalysts for use in forming these polymers. Despite the fact that a reaction somewhat analogous to polyesteriiication is involved, it has been found that conventional catalysts, such as manganese formate, are not active in reactions for producing the aforesaid polymers, although they are highly effective in forming polyesters from, for example, terephthalic acid and ethylene glycol. Catalysts, such as lead oxide, boron and others have been previously employed in forming the polyesteramides to which this invention is addressed, but they have not possessed the necessary activity for satisfactory results. That is, when employed, the polymerization reaction, which is conducted at high temperatures, must be so prolonged in order to obtain the desired degree of polymerization for polymers having fiber-forming characteristics that the polymers become degraded and develop undesirable color.

Accordingly, it is an object of this invention to provide an improved process for preparing polyesteramides from terephthalic acid diamide-N,N'-di-e-caproic acid or the ester derivatives thereof and a glycol.

It is a further object of this invention to provide a novel catalytic agent for use in the afore-mentioned process.

.It is a still further object to provide a process for pre paring polyesteramides of the'just described class with an improved color and a higher molecular weight.

Other objects will be apparent from the description and claims which follow.

In general, these objects are accomplishedby conducting a condensation reaction between terephthalic .acid diamide-N-N-di-e-caproic acid or dialkyl ester derivatives thereof with a glycol containing 2 to carbon atoms in the presence of a catalytic amount of cadmium acetate;

The dialkyl ester derivatives referred to above are diesters formed from lower alcohols, such as methy1-, ethyl, propyl-, butyl-, and amyl-alcohol as well as the corresponding mixedesters. The glycols employed are aliphatic containing from2 to 10 carbon atoms. Ethylene glycol is of particular preference and hereinafter will be specifical- 1y mentioned when reference is made to glycols.

In the preparation of these polymers, the reactive intermediate, i.e., the di-glycol ester of terephthalic acid diamide-N,N'-di-e-caproic acid must be first obtained and y then polymerized. When employing the terephthalic acid diamide-N,N-di-e-caproic acid per se as a starting material, the polymer preparation is conducted in two stages, both in the presence of the catalytic agent cadmium acetate. In the first stage, the acid is reacted with an amount ice of ethylene glycol which exceeds the stoichiometric quantity to form the di-glycol ester of the acid. This monomer is then poly-condensed in the second stage reaction to form the polymer. The amount of ethylene glycol employed in this reaction is not critical beyond the requirement that at least more than a stoichiometric quantity be present. Generally, however, high proportions of the glycol relative to the esters or acids are used. For example, up to 10 times as many moles of glycol as ester or acid may be employed because the reaction takes place more readily in the presence of an excess of glycol.

The conditions necessary for these reactions are well known and will be readily understood by those skilled in the art. Thus, during the first stage in which the di-glycol ester is formed, the reaction is carried out at atmospheric pressure and at a temperature in the range of from about 175 to 195 C. and preferably between 180 and 190C.

At the completion of the first stage, the excess glycol is distilled oil prior to entering the second stage'of polycondensation. Thereafter, in the second or polymerizai tion stage the reactive intermediate, e.g., the bis-2-hydroxyethyl ester of terephthalic acid diamide-N,N-di-e-caproic acid is heated at a still higher temperature of from about 230 to 250 C. and under reduced pressure within the range of from 0.1 to 5 mm. of mercury to form the polymer. The second or polymerization step is continued, if a fiber-forming polymer is desired, until the reaction product has the desired degree of polymerization, which may be determined by viscosity measurements. Normally, high molecular weight polymers in the fiber-forming range can'be obtained in from about minutes to one hour of polymerization reaction time.

When employing the dialkyl esters of terephthalic acid diamide-N,N'-di-e-caproic acid as a starting material, the procedural steps are essentially the same as outlined above. In the first stage, an. ester-interchange reaction is conducted between ethylene glycol and the dialkyl ester, for example, the dimethyl ester of terephthalic acid diamide- N,N-di-e-caproic acid at normal pressures anda temperature of between 175 to 195 C. The di-glycol ester of terephthalic acid diamide-N,N'-di-e caproic acid is formed during this reaction together with methanol which is removed from the reaction zone. The second, or polycondensation stage, is conducted atreduced pressures of from 0.1 to-5 mm. of mercury at a temperature in the hour.

As has been noted, the cadmium acetate catalyst is present in both the first and second reaction steps which have been described above. The amount of catalyst present may be widely varied and is not critical. All that is needed is a catalytic amount. For example, good results can be obtained with a catalyst concentration varying between 0.001 to 2.0 percent by weight based on the terephthalic acid diamide-N,N'-di-e-caproic acid or the dialkyl ester derivatives thereof, with from about 0.1 to 0.5 percent being of preference.

Of course, as will be recognized by those skilled in the art, the reactive intermediate whilch is polymerized to obtain the polymer may be prepared separately from the polymer forming reaction and used at a later time. It

may also be prepared by other means than discussed above, for. example, by reacting terephthalic acid diamide- N,N'-di-s-caproic acid with ethylene oxide. Usually, however, this intermediate is obtained in the manner described. Regardless of how the reactive intermediate is obtained, the polymerization reaction to form the polymer I is greatly accelerated in the presence of the novel cadmium acetate catalyst of this invention, and the high molecular weight polymer obtained is substantially free from color.

Specific viscosity,'as employed herein, is represented by the formula N sp Re1. 1 where N Time of new of the polymer solution in seconds Time of flow of the solvent in seconds Viscosity determination on the polymer solutions and solvent are made by allowing said solutions and solvent to flow by gravity at 25 C- through a capillary tube. In a all determinations, the polymer solutions contained 0.55 percent by weight of the polymer dissolved in a solvent mixture containing 60 percent by weight of phenol and 40 percent by weight of tetrachloroethane.

Example I This example illustrates the formation of a polymer from terephthalic acid diamide-N,N'-di-e-caproic acid dimethyl ester by employing a representativecatalyst of the prior practice, i.e., lead oxide.

35 parts of the dimethyl ester of terephthalic acid diamide-N,N-di-e-caproic acid, 15 parts of ethylene glycol and 0.2 part of yellow lead oxide were heated with stirring and in a nitrogen atmosphere to a temperature of between 190 and 200 C. for a period of about 45 minutes at which time the trans-esterification was complete. The resulting bis 2-hydroxyethyl) ester of terephthalic acid diamide-N,N.-di-e-caproic acid was then heated to a temperature of between 230 and 240 C. at a reduced pressureof 0.2 mm.'of mercury. These conditions were maintained for a period of four and one-half hours. The polymer recovered had a specific viscosity of 0.49 and was badly discolored.

Example II This example illustrates the, practice of this invention wherein terephthalic acid diamide-N,N-di-e-caproic acid dimethyl esterwas used as a starting material.

35 parts of the dimethyl ester of terephthalic acid diamide-N,N'-di-e-caproic acid, 20 parts of ethylene glycol and 0.7 part of cadmium acetate (Cd(C H O) were heated at a temperature of from 185 to 192 C. at atmospheric pressure for one hour. During this trans-esterification reaction, methanol was continuously taken on overhead. The temperature was then raised to about 245 C. inorder to distill oii exces glycol, The resulting bis(2- hydroxyethyl) ester of terephthalic acid diamide-N,N'-die-caproic acid was then condensed with stirring at 240 to 245 vC. and under a reduced pressure of 0.2 mm. of mercury. After permitting this poly-condensation reaction to run for one hour, a polymer wasrecovered which had a specificviscosity of 0.60.

Example III stirring for 75 minutes. The reaction temperature was then raised to about 245 C. in order to distill off the excess gylcol. The resulting bis(2-hydroxyethyl) ester of terephthalic acid diamide-N,N-di E-caproic acid was then heated to a temperature of from 240 to 245 C. at a reduced pressure of 0.2 mm. of mercury. After permitting of the poly-condensation reaction to continue for 74 minutes, a polymer was recovered which had a specific viscosity of 0.85. Fibers were fabricated from the polymer by extruding a sample of the same through a conventional spinnerette. The spinning conditions employed were a melt temperature of 245 C., spinnerette temperature of 245 C. and an extrusion pressure of 195 p.s.i.g.

It is observed that in Example I above where a representative catalyst of the prior art was employed in the polymer preparation, four and one-half hours reaction time under poly-condensation conditions were required to produce a polymer having a specific viscosity of 0.49. On the other hand, in Example II Where the catalyst of this invention was employed, a polymer was recovered after only one hour of reaction time with a specific viscosity value of 0.60 as determined under the identical conditions. The same order of improvement in the rate of reaction over the control, Example I, is shown in Example III.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be e'fiected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

I. A process for preparing poiyesterarnides which cornprises conducting a condensation reaction of an aliphatic glycol containing 2 to 10 carbon atoms with a compound selected from the group consisting of terephthalic acid diamide-N,N'-di-s-caproic acid and the lower dialkyl esters thereof in the presence of a catalytic amount of cadmium acetate.

2. A process for producing polyesteramides which comprises conducting an ester-interchange between ethylene glycol and the dimethyl ester of terephthalic acid diamide-N,N-di-e-caproic acid to form the bis(2-hydroxyethyl) ester of terephthalic acid diamide-N,N'-di-e-caproic acid and subsequently poly-condensing said bis(2-hydroxyethyl) ester of terephthalic acid diamide-N,N'-di-ecaproic acid, both the ester-interchange and poly-condensation reactions being conducted in the presence of from 0.001 to 2.0 Weight percent of cadmium acetate based on the weight of said dimethyl ester of terephthalic acid diamide-N,N'-di-e-caproic acid.

3. A process for preparing the bis(2-hydroxyethyl) ester of terephthalic acid diamide-N,N'-di-e-caproic acid comprising reacting ethylene glycol and terephthalic acid diarnide-I LN-di -s-caproic acid together in the presence of rorn about 0.001 to 2.0 Weight percentof cadmium acetate based on the weight of said terephthalic acid diamide- N, N'-di-e-caproic acid reactant.

4. A process for preparing the bis(2-hydroxyethyl) ester of terephthalic acid diarnide-N,N-.li-e-caproic acid comprising reacting ethylene glycol andthe dimethyl ester of terephthalic acid diamide-N,N-di-e-caproic acid together in the presence of from about 0.001' to 2.0 weight percent of cadmium acetate based on the weight of said dimethyl ester of terephthalic acid diamide-lLNdi-scaproic acid.

5. A process for producing polyesterarnides which comprises polymerizing the bis(2-hydroxyetl1yl)ester of terephthalic acid diamide-N,N-di-e-caproic acid in the presence of a catalytic amount'of cadmium acetate.

6. A process for preparing polyesteramides which comprises the following steps in sequence: (1) causing a compound selected from the group consisting of terephthalic acid diamide-N,N-dicaproic acid and the dimethyl ester thereof to react with a quantity of ethylene glycol in'excess of the stoichiometric amount at a temperature in the range of from to C., (2) there after continuing the reaction under poly-condensation conditions of a reduced pressure in the range of from 0. l.to 5 mm. of mercury and a temperature of from 230 to 250 C., With steps (1) and (2) being conducted in the presence of a catalytic amount of cadmium acetate. 7. A process for preparing polyesteramides which comprises the following steps in sequence: (1) causing terephthalic acid diamide-N,N'-di-e-caproic acid to react with a quantity of ethylene glycol in excess of the stoichiometric amount at a temperature in the range of from 175 to 195 C., (2) thereafter continuing the reaction under poly-condensation conditions of a reduced pressure in the range of from 0.1 to 5 mm. of mercury and a temperature of from 2309 to 250 C., with steps (1) and (2) being conducted in the presence of from 0.001 to 2.0

weight percent of cadmium acetate based on the weight of said terephthalic acid diamide-N,N'-di-e-caproic acid reactant.

8. A process for preparing polyesteramides which comprises the following steps in sequence: (1) causing the dimethyl ester of terephthalic acid diarnide-N,N'-die-caproic acid to react with a quantity of ethylene glycol 6 in excess of the stoichiometric amount at a temperature in the range of from to (3., (2) thereafter continuing the reaction under poly-condensation conditions of a reduced pressure in the range of from 0.1 to 5 mm.

of mercury and a temperature of from 230 to 250 C., V

with steps (1) and (2) being conducted in the presence of from 0.001 to 2.0 Weight percent of cadmium acetate based on the weight of said terephthalic acid diarnide- N,N-di-e-caproic acid reactant.

References Cited in the file of this patent UNITED STATES PATENTS Belgium Dec. 31, 1953 

1. A PROCESS FOR PREARING POLYESTERAMIDES WHICH COMPRISES CONDUCTING A CONDENSATION REACTION OF AN ALIPHATIC GLYCOL CONTAINING 2 TO 10 CARBON ATOMS WITH A COMPOUND SELECTED FROM THE GROUP CONSISTING OF TEREPHTHALIC ACID DIAMIDE-N,N''-DI-E-CAPROIC ACID AND THE LOWER DIALKYL ESTERS THEREOF IN THE PRESENCE OF A CATALYTIC AMOUNT OF CADMIUM ACETATE. 